1. Field of the Invention
The present invention generally relates to a semiconductor package and a method for manufacturing the semiconductor package, and more particularly to a chip scale package and a method for manufacturing the chip scale package at the wafer level, using a redistribution substrate.
2. Description of the Related Arts
The electronics industry has been progressing with the miniaturization of electronic devices. This trend influences semiconductor packaging technology, which enables the connection between bare IC chips and other components. Typically, a semiconductor package has a footprint much larger than that of the chip. To adapt to the miniaturization trend, the size difference between the package and the chip has been reduced, producing a new package type called a Chip Scale Package (or a Chip Size Package) (CSP). Among the manufacturing technologies for the CSPs is Wafer Level Chip Scale Packaging, which assembles CSPs at the wafer level, rather than separately processing individual chips.
FIG. 1 schematically shows a semiconductor wafer 10, which includes integrated circuit chips 20 and scribe lines 14 dividing the chips 20. As shown in FIG. 2 which is an enlarged view of part `A` of FIG. 1, chip pads 22 are on each chip 20, and a passivation layer 24 covers the upper surface of the IC chip 20 except where openings through which the passivation layer 24 expose the chip pads 22.
Regarding to FIGS. 3 and 4, in conventional wafer level chip scale packaging, a dielectric layer 36 and solder bumps 38 are formed on the surface of the wafer 10. The solder bumps 38 electrically connect to the chip pads 22 of FIG. 2. Then, a sawing apparatus separates the wafer 10 along the scribe lines 14, producing individual CSPs 30.
FIG. 4 illustrates the cross-sectional structure of the CSP 30. The solder bump 38 connects to the chip pad 22 through a metal layer 34, and a first and a second dielectric layers 32 and 36 are respectively on and under the metal layer 34. Integrated circuits (not shown) are under the chip pad 22 and the passivation layer 24. In the fabrication of the CSPs 30 on the wafer 10, the first dielectric layer 32 is formed and patterned on the wafer 10 such that openings in the first dielectric layer 32 expose the chip pads 22. Then, the metal layer 34 is formed on the first dielectric layer by metal deposition and patterning, so that the metal layer 34 contacts the chip pads 22. The second dielectric layer 36 is formed on the metal layer 34 such that openings in the second dielectric layer 36 expose a portion of the metal layer 34. Finally, solder bumps 38 are formed on the exposed portion of the metal layer 34. As described above, sawing separates individual CSPs 30.
The CSPs manufactured by the above-described manufacturing method have several problems. First, coating and high-temperature curing of the dielectric layers may apply thermal stress to the integrated circuits below the dielectric layers, damaging the integrated circuits. The thinner the dielectric layers are, the smaller the thermal stress is. However, making the dielectric layer thin increases the capacitance of the CSP. Second, when the CSP is mounted on an external circuit board such that the solder bumps contact the circuit board, the connection integrity between the solder bumps and the circuit board is not reliable.
Third, since defective chips as well as good chips are packaged in wafer level, the manufacturing cost of individual CSPs increases.